A major contradiction

In the bible there is a passage where a jail keeper asks Paul and Silas what he has to do to be “saved.” They tell him to confess that jesus is lord and believe that god raised him from the dead. hmmm okay but in a different passage it says that “even the demons believe and tremble.” So I guess that’s not all you have to do to be saved. And if demons are capable of “sinning” then they should also be able to receive “divine forgiveness” and “salvation.” Hypothetically though because they don’t exist.